This invention relates to high pressure packings and more particularly to a packing assembly for use as a shaft seal such as the seal between the stem and bonnet of a gate valve.
The various types of packing materials and valve stem packing arrangements that have been proposed or used in the past for high pressure applications or applications where the valve is subjected to handling wide pressure variations or harmful noxious or toxic substances such as hydrogen sulfide have not been entirely satisfactory. In assembly of the valves, it is frequently important that the packings be placed in a preloaded condition prior to use in order that a seal can be established at low fluid pressures as the pressure builds. This has heretofore been very difficult to achieve, and installation and removal of such packings have been difficult. Tolerance stack-up has presented a problem with packings of the type which use spring washers for preloading since a varying number of such springs must be employed with different valves or valve bodies due to manufacturing variances. The determination of the proper number of such springs is tedious and time consuming when done by field personnel in repairing and replacing packings and can lead to hazardous errors. Also, such non-uniformity obviously adds to the manufacturing costs. Furthermore, replacement of such packings is not always easy and it is also very difficult, it not impossible, to adjust or readjust the preloading of the packing assembly when the valve is in service.
It is, therefore, an object of the invention to provide a pressure energizable packing assembly for sealing the stem and bonnet of a high pressure gate valve and which can be manufactured and assembled economically as a cartridge.
Another object is to provide a packing assembly for effecting a shaft seal between a shaft and the wall of a bore which receives the shaft therethrough wherein the packing assembly is provided with annular packing elements and a fixed limited number of annular springs for applying an axial loading to the packing elements, the packing assembly being adapted for use in packing chambers having considerable variation in axial dimensions as results from stacking of tolerances.
Still another object is to provide a packing assembly for effecting a seal between the valve stem and bonnet of a gate valve which can be installed and placed in a preloaded condition and is provided with means for easily adjusting the preloading condition of the packing assembly without requiring the removal of the packing assembly while the valve is in operation.
A further object is to provide a pressure energizable packing assembly for sealing the stem and bonnet of a high pressure gate valve wherein the assembly comprises redundant sets of packing rings arranged in a cartridge wherein fluid pressure in the valve body is amplified in transmission to the packing rings even though there is a sealing failure of one set of packing rings.
A still further object is to provide an improved packing assembly for sealing between the valve stem and body of a high pressure valve and which can be easily adjusted or replaced in the field by service personnel.